1. Field of the Invention
The present invention relates to methods and systems for image-guided effector placement. Methods and systems of the invention enable minimally invasive image-guided interventions with a single cross-sectional image and without the use of a sterotactic frame or separate fiducial apparatus. Preferred systems of the invention include a localization module, integrated with a medical instrument, that allows for localization of the effector in targeted image space using a single cross-sectional image.
2. Background
Percutaneous procedures, i.e. through the skin procedures, require one to find the position of an internal target, e.g. organ, tumor, etc., without direct visualization. Most often, this involves registration of an image data set, in which the target is identified, with physical space. This procedure, stereotaxy, was reported early by Clarke and Horsley (Clarke, Brain (1905) 28:12-29). Most techniques have been based upon the attachment of a rigid frame to a patient, providing a common coordinate system through which the image and physical spaces can be related (Galloway, in Interactive Image-Guided Neurosurgery. American Association of Neurologic Surgeons (1993) 9-16). While stereotactic procedures were initially advanced using two-dimentional imaging modalities, the advent of three dimensional imaging systems including Computed Tomography (CT) in the 1970's greatly accelerated development and applications. Instead of projecting three-dimensional structures into two-dimensions, this modality provides a series of 2D image slices, allowing for true three-dimensional reconstruction.
The Brown-Roberts-Wells (BRW) frame consisting of three N shaped motifs attached to a patient's skull, represented a major advance in localization (Brown, Invest Radiol (1979) 14:300-304). Previous frames were constrained to remain strictly perpendicular to the image plane, providing little flexibility (Galloway, in Interactive Image-Guided Neurosurgery. American Association of Neurologic Surgeons (1993) 9-16). However, the BRW frame was more versatile in that the position and orientation of the frame was fully encoded within each image slice such that the position of a point was defined in both the frame space and the image space coordinate systems allowing for rotations and tilting of the frame relative to the image plane (Brown, Invest Radiol (1979) 14:300-304).
A number of systems use a rigid stereotaxic frame wherein the frame is attached to the patient. These devices tend to be large and unwieldy contraptions that limit the effective application time of the frame to less than a day. Consequently, the frame must be recalibrated before each use. A system was implemented for image guide intracranial needle placement using biplanar x-ray and a fixed head frame (Lavallee, Computer Integrated Surgery: Technology and Clinical Applications, (1996) p 343-351). In another neurosurgical system, a surgical plan using multiple CT image slices, register by docking their robot with the patient's stereotactic head frame, and then place the needle without CT surveillance (Kwoh, IEEE Trans Biomed Eng (1988) 35:153-160). In another system a stereotactic head frame is used to register the robot and image space, but are able to perform needle placement under active CT surveillance to confirm the position of their end effector (Glauser, Second Annual International Symposium on MRCAS (November 1995)). Similarly, a method wherein the placement and register of a needle under biplanar fluoroscopy, was developed in order to access mobile organs (e.g. the kidneys) (Bzostek et al. The First Joint Conference of CVRMed and MRCAS, (March 1997) Grenoble, France).
Surgically implanted fiducial markers have been employed to generate reference frame in the patient and have been affixed to the bones, in particular the cranium, to prevent the marker from shifting with time. These implant systems have been used for image-guided applications in the brain where the cranium is readily accessible for surgical implantation of fiducial markers. Surgical pins and screws for permanently affixing fiducial implants to a patient bone are reported in U.S. Pat. Nos. 5,397,329 and 5,636,255 such that pegs, pins or screws comprising a scanner opaque object are surgically implanted into one or more bones such as the cranium, sternum or vertabrae. Fiducial markers that are implanted into the patient's soft tissue are reported in U.S. Pat. Nos. 5,941,890 and 6,056,700.
While these implanted markers are fixed within the body and are unlikely to move, there are several drawbacks to their use. Implantation requires surgery wherein the markers are inserted or driven into the bones raising the concern of cracking or otherwise damaging the support bone in the implantation process. Further surgical procedures increase patient discomfort, hospital stays or recovery time and the risk of complications such as infection or bone damage.
It thus would be desirable to have improved methods and systems to determine the location of an end effector delivery system and the location of an effector such as a needle, probe, etc. within a body. It would be further desirable to have such a position and orientation system that could be employed in minimally invasive surgical procedures without need for external reference frames, surgically implanted fiducial markers or calibration procedures.